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Tartışma:Haplogroup
In the study of molecular evolution, a haplogroup (from the , haploûs, "onefold, single, simple") is a group of similar haplotypes that share a common ancestor with a single nucleotide polymorphism (SNP) mutation. Because a haplogroup consists of similar haplotypes, this is what makes it possible to predict a haplogroup from haplotypes. An SNP test confirms a haplogroup. Haplogroups are assigned letters of the alphabet, and refinements consist of additional number and letter combinations, for example R1b1. Y-chromosome and mitochondrial DNA haplogroups have different haplogroup designations. Haplogroups pertain to deep ancestral origins dating back thousands of years.The International Society of Genetic Genealogy see Haplogroup definition in DNA-NEWBIE GLOSSARY http://www.isogg.org In human genetics, the haplogroups most commonly studied are Y-chromosome (Y-DNA) haplogroups and mitochondrial DNA (mtDNA) haplogroups, both of which can be used to define genetic populations. Y-DNA is passed solely along the patrilineal line, from father to son, while mtDNA is passed down the matrilineal line, from mother to offspring of both sexes. Neither recombines, and thus Y-DNA and mtDNA change only by chance mutation at each generation with no intermixture between parents' genetic material. Haplogroup formation Mitochondria are small organelles that lie in the cytoplasm of eucaryotic cells, such as those of humans. Their primary purpose is to provide energy to the cell. Mitochondria are thought to be reduced descendants of symbiotic bacteria that were once free living. One indication that mitochondria were once free living is that each contains a circular DNA, called mitochondrial DNA (mtDNA), whose structure is more similar to bacteria than eukaryotic organisms (see endosymbiotic theory). The overwhelming majority of a human's DNA is contained in the chromosomes in the nucleus of the cell, but mtDNA is an exception. An individual inherits their cytoplasm and the organelles it contains exclusively from their mother, as these are derived from the ovum (egg cell), sperm only carry chromosomal DNA due to the necessity of maintaining motility. When a mutation arises in mtDNA molecule, the mutation is therefore passed in a direct female line of descent. These mutations are derived from copying mistakes, when the DNA is copied it is possible that a single mistake occurs in the DNA sequence, these single mistakes are called single nucleotide polymorphisms (SNPs). Human Y chromosomes are male-specific sex chromosomes; nearly all humans that possess a Y chromosome will be morphologically male. Y chromosomes are therefore passed from father to son; although Y chromosomes are situated in the cell nucleus, they only recombine with the X chromosome at the ends of the Y chromosome; the vast majority of the Y chromosome (95%) does not recombine. When mutations (SNPs) arise in the Y chromosome, they are passed on directly from father to son in a direct male line of descent. The Y chromosome and mtDNA therefore share specific properties. Other chromosomes, autosomes and X chromosomes in women, share their genetic material (called crossing over leading to recombination) during meiosis (a special type of cell division that occurs for the purposes of sexual reproduction). Effectively this means that the genetic material from these chromosomes gets mixed up in every generation, and so any new mutations are passed down randomly from parents to offspring. The special feature that both Y chromosomes and mtDNA display is that mutations can accrue along a certain segment of both molecules and these mutations remain fixed in place on the DNA. Furthermore the historical sequence of these mutations can also be inferred. For example, if a set of ten Y chromosomes (derived from ten different men) contains a mutation, A, but only five of these chromosomes contain a second mutation, B, it must be the case that mutation B occurred after mutation A. Furthermore all ten men who carry the chromosome with mutation A are the direct male line descendants of the same man who was the first person to carry this mutation. The first man to carry mutation B was also a direct male line descendant of this man, but is also the direct male line ancestor of all men carrying mutation B. Series of mutations such as this form molecular lineages. Furthermore each mutation defines a set of specific Y chromosomes called a haplogroup. All men carrying mutation A form a single haplogroup, all men carrying mutation B are part of this haplogroup, but mutation B also defines a more recent haplogroup (which is a subgroup or subclade) of its own which men carrying only mutation A do not belong to. Both mtDNA and Y chromosomes are grouped into lineages and haplogroups; these are often presented as tree like diagrams. Haplogroup population genetics It is usually assumed that there is little natural selection for or against a particular haplotype mutation which has survived to the present day, so apart from mutation rates (which may vary from one marker to another) the main driver of population genetics affecting the proportions of haplotypes in a population is genetic drift — random fluctuation caused by the sampling randomness of which members of the population happen to pass their DNA on to members of the next generation of the appropriate sex. This causes the prevalence of a particular marker in a population to continue to fluctuate, until it either hits 100%, or falls out of the population entirely. In a large population with efficient mixing the rate of genetic drift for common alleles is very low; however, in a very small interbreeding population the proportions can change much more quickly. The marked geographical variations and concentrations of particular haplotypes and groups of haplotypes therefore witness the distinctive effects of repeated population bottlenecks or founder events followed by population separations and increases. The lineages which can be traced back from the present will not reflect the full genetic variation of the older population: genetic drift means that some of the variants will have died out. The cost of full Y-DNA and mtDNA sequence tests has limited the availability of data; however, their cost has dropped dramatically in the last decade. Haplotype coalescence times and current geographical prevalences both carry considerable error uncertainties. This is especially troublesome for coalescence times, because most population geneticists still continue (albeit decresing a little bit) to use the "Zhivotovski method", which is heavily criticised by DNA-genealogists for its' falsehood. Human Y-chromosome DNA haplogroups Human Y chromosome DNA (Y-DNA) haplogroups are named from A to T, and are further subdivided using numbers and lower case letters. Y chromosome haplogroup designations are established by the Y Chromosome Consortium.Y Chromosome Consortium Y-chromosomal Adam is the name given by researchers to the male who is the most recent common patrilineal (male-lineage) ancestor of all living humans. Major Y-chromosome haplogroups, and their geographical regions of occurrence (prior to the recent European colonization), include: See also *International HapMap Project *Molecular evolution *Molecular systematics *Molecular phylogeny *Haplotype *Genetic genealogy *Genealogical DNA test *Genetics *List of genetic genealogy topics *List of haplogroups of historical and famous figures ** (haplogroup) References External links General *World Families Network *Haplogroups.com *The Genographic Project News *Indian maternal gene pool, Journal of Human Genetics'' *Dienekes' Anthropology Blog frequent highlights of new results. all DNA haplogroups *http://www.scs.uiuc.edu/~mcdonald/WorldHaplogroupsMaps.pdf Y chromosome DNA haplogroups *Y Chromosome Consortium *ISOGG Y-DNA Haplogroup Tree 2006 *DNA Heritage's Y-haplogroup map *Haplogroup Predictor *The Y Chromosome Consortium (2002), A Nomenclature System for the Tree of Human Y-Chromosomal Binary Haplogroups, Genome Research, Vol. 12(2), 339-348, February 2002. (Detailed hierarchical chart has conversions from previous naming schemes) *DNA Consulting's Conversion Chart for Male Haplogroups (PDF) *Semino et al. (2000), The Genetic Legacy of Paleolithic Homo sapiens sapiens in Extant Europeans, Science, Vol 290 (paper which introduced the "Eu" haplogroups). Mitochondrial DNA haplogroups *HaploGrep - automatic classification of mitochondrial DNA haplogroups *graphical mtDNA haplogroup skeleton *The Making of the African mtDNA Landscape *Do the Four Clades of the mtDNA Haplogroup L2 Evolve at Different Rates? ca:Haplogrup cv:Гаплоушкăн cs:Haploskupina de:Haplogruppe el:Απλοομάδα es:Haplogrupo fa:تک‌گروه fr:Haplogroupe ko:하플로그룹 hr:Haploskupina it:Aplogruppo nl:Haplogroep no:Haplogruppe oc:Aplogrop pl:Haplogrupa pt:Haplogrupo ru:Гаплогруппы fi:Haploryhmä sv:Haplogrupp zh:单倍群